1. Field of the Invention
This invention relates to a valve operator for a plug-type valve, and particularly, to a valve operator employing balanced rollers within a clutch-type mechanism for opening and closing the valve.
2. Background Discussion
U.S. Pat. No. 2,795,960 discloses a valve operator used with a plug-type valve. This valve operator is designed to lift a plug from a seat within the body of the plug-type valve and then rotate the plug 90 degrees. This moves the plug from a closed position to a position which opens the valve.
A clutch-type mechanism is employed to allow a sleeve attached to the plug to move linearly, lifting the plug from the seat, by rotating a spindle. A single roller element is carried in the sleeve which is threadably connected to the spindle. The roller element moves in a groove in the housing of the valve operator until it is adjacent a recess in the spindle. When the roller element is adjacent the recess, further rotation of the spindle results in rotation of the sleeve rather than linear movement. This in turn rotates the plug within the valve body.
The problem in employing this clutch-type mechanism is that, when heavy loads are encountered, the roller element slips, scoring the groove and the wall adjacent the recess in the spindle. This scoring over several years eventually results in the valve operator becoming inoperable.